Dihydropyridines and atypical MDR: A novel perspective of designing general reversal agents for both typical and atypical MDR

Unsymmetric dihydropyridines bearing 2-pyridyl methyl carboxylate as modulators of P-glycoprotein; synthesis and biological evaluation in resistant and non-resistant cancer cells

Multi-drug resistance (MDR) in cancer cells is often associated with overexpression of P-glycoprotein (P-gp or ABCB1 or MDR1); therefore, modulators of this transporter might be helpful in overcoming MDR. In this study, 16 novel unsymmetrical dihydropyridine (DHP) derivatives bearing 2-pyridyl methyl carboxylate at C3 and a nitroimidazole or nitrophenyl ring at C4 positions of the DHP ring were synthesized. Their cytotoxicity was tested against four human cancer cells by MTT assay. The reversal capacity of MDR was examined in P-gp overexpressing cells (MES-SA/DX5) by measuring the alteration of doxorubicin’s IC50 and performing flow cytometric determination of intracellular rhodamine 123 accumulation. The calcium channel blocking (CCB) activity, as a side effect of DHPs, was tested on the ileum of a guinea pig. Molecular docking was performed to explain the binding mode of compounds. Two derivatives, 4a and 4c, containing 4-nitrophenyl at C4 and possessing methyl (4a) and iso-propyl (4c) carboxylates at the C5 position of DHP core demonstrated superior cytotoxic and MDR reversal activities and lower CCB effect. Docking analysis confirmed the importance of the 4-nitrophenyl ring for P-gp inhibitory activity. Some of the synthesized DHP derivatives with considerable MDR reversal capacity could be promising compounds for further discovery of useful agents for management of drug resistant cancer.

Bactericidal and immunomodulatory properties of magnetic nanoparticles functionalized by 1,4-dihydropyridines

Background

1,4-Dihydropyridine (1,4-DHP) and its derivatives are well-known calcium channel blockers with antiarrhythmic and antihypertensive activities. These compounds exhibit pleiotropic effects including antimicrobial activities that rely on their positive charge and amphipathic nature. Use of magnetic nanoparticles (MNPs) as carriers of 1,4-DHP modulates their properties and enables improved formulations with higher efficacy and less toxicity.

Methods

In this study, the antimicrobial and immunomodulatory activities of novel 1,4-DHP derivatives in free form and immobilized on MNPs were determined by evaluating pathogen outgrowth and proinflammatory cytokine release in experimental settings that involve incubation of various 1,4-DHPs with clinical isolates of bacteria or fungi as well as mammalian cell culture models.

Results

Conventional immobilization of 1,4-DHP on aminosilane-coated MNPs markedly enhances their antimicrobial activity compared to nonimmobilized molecules, in part because of the higher affinity of these nanosystems for bacterial cell wall components in the presence of human body fluids.

Conclusion

Optimized nanosystems are characterized by improved biocompatibility and higher anti-inflammatory properties that provide new opportunities for the therapy of infectious diseases.

The cytotoxic effects of VE-3N, a novel 1,4-dihydropyridine derivative, involve the mitochondrial bioenergetic disruption via uncoupling mechanisms

Several 1,4-dihydropyridine derivatives overcome the multidrug resistance in tumors, but their intrinsic cytotoxic mechanisms remain unclear. Here we addressed if mitochondria are involved in the cytotoxicity of the novel 1,4-dihydropyridine derivative VE-3N [ethyl 6-chloro-5-formyl-2-methyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3-carboxylate] towards cancer cells by employing hepatic carcinoma (HepG2) cells and isolated rat liver mitochondria. In HepG2 cells, VE-3N induced mitochondrial membrane potential dissipation, ATP depletion, annexin V/propidium iodide double labeling, and Hoechst staining; events indicating apoptosis induction. In isolated rat liver mitochondria, VE-3N promoted mitochondrial uncoupling by exerting protonophoric actions and by increasing membrane fluidity. Mitochondrial uncoupling was evidenced by an increase in resting respiration, dissipation of mitochondrial membrane potential, inhibition of Ca²⁺ uptake, stimulation of Ca²⁺ release, decrease in ATP synthesis, and swelling of valinomycin-treated organelles in hyposmotic potassium acetate media. Furthermore, uncoupling concentrations of VE-3N in the presence of Ca²⁺ plus ruthenium red induced the mitochondrial permeability transition process. These results indicate that mitochondrial uncoupling is potentially involved in the VE-3N cytotoxic actions towards HepG2 cells. Considering that hepatocellular carcinoma is the most common form of liver cancer, our findings may open a new avenue for the development of VE-3N-based cancer therapies, and help to unravel the cytotoxic mechanisms of 1,4-dihydropyridines towards cancer cells.

Novel 5-oxo-hexahydroquinoline derivatives: design, synthesis, in vitro P-glycoprotein-mediated multidrug resistance reversal profile and molecular dynamics simulation study

Overexpression of the efflux pump P-glycoprotein (P-gp) is one of the important mechanisms of multidrug resistance (MDR) in many tumor cells. In this study, 26 novel 5-oxo-hexahydroquinoline derivatives containing different nitrophenyl moieties at C₄ and various carboxamide substituents at C₃ were designed, synthesized and evaluated for their ability to inhibit P-gp by measuring the amount of rhodamine 123 (Rh123) accumulation in uterine sarcoma cells that overexpress P-gp (MES-SA/Dx5) using flow cytometry. The effect of compounds with highest MDR reversal activities was further evaluated by measuring the alterations of MES-SA/Dx5 cells’ sensitivity to doxorubicin (DXR) using MTT assay. The results of both biological assays indicated that compounds bearing 2-nitrophenyl at C₄ position and compounds with 4-chlorophenyl carboxamide at C₃ demonstrated the highest activities in resistant cells, while they were devoid of any effect in parental nonresistant MES-SA cells. One of the active derivatives, 5c, significantly increased intracellular Rh123 at 100 µM, and it also significantly reduced the IC₅₀ of DXR by 70.1% and 88.7% at 10 and 25 µM, respectively, in MES-SA/Dx5 cells. The toxicity of synthesized compounds against HEK293 as a noncancer cell line was also investigated. All tested derivatives except for 2c compound showed no cytotoxicity. A molecular dynamics simulation study was also performed to investigate the possible binding site of 5c in complex with human P-gp, which showed that this compound formed 11 average H-bonds with Ser909, Thr911, Arg547, Arg543 and Ser474 residues of P-gp. A good agreement was found between the results of the computational and experimental studies. The findings of this study show that some 5-oxo-hexahydroquinoline derivatives could serve as promising candidates for the discovery of new agents for P-gp-mediated MDR reversal.

Synthesis of 6-alkylsulfanyl-1,4-dihydropyridines as potential multidrug resistance modulators

6-Alkylsulfanyl-1,4-dihydropyridines

4-isoxazolyl-1,4-dihydropyridines: a tale of two scaffolds

The association of the isoxazole and dihydropyridine (DHP) ring systems fused at the 4'-isoxazolyl- to the 4-position of the DHP has produced a combination scaffold, the isoxazolyl-DHPs (IDHPs) with unique conformational characteristics. The IDHPs are useful in probing biological activity, as exemplified by our efforts in the fields of voltage gated calcium channel (VGCC) antagonists and inhibitors of the multi-drug resistance (MDR) transporter. A strategically placed methyl group produced a signifcant change at the VGCC, with (R)-(+)-1-phenyl-prop-2-yl (3.7 nM) > phenethyl (22.9 nM) > (S)-(-)-1-phenyl-prop-2-yl (210 nM), a eudismic ratio of 56.7. Branching at the C-5 of the isoxazole produced a 25% increase in MDR binding, and replacing the DHP C-3 ester with a functionalized amide also gave a dramatic increase in binding affinity. Opportunities for combined scaffolds - including examples containing IDHPs - are waiting to be discovered: because new biology is driven by new chemistry.

Construction of 3,5-dinitrated 1,4-dihydropyridines modifiable at 1,4-positions by a reaction of β-formyl-β-nitroenamines with aldehydes

A novel and efficient method for the synthesis of 4-substituted 3,5-dinitro-1,4-dihydropyridines by a reaction of β-formyl-β-nitroenamines with aldehydes was developed.

Fluorescent probes of the isoxazole-dihydropyridine scaffold: MDR-1 binding and homology model

Isoxazole-1,4-dihydropyridines (IDHPs) were tethered to fluorescent moieties using double activation via a lanthanide assisted Weinreb amidation. IDHP-fluorophore conjugate 3c exhibits the highest binding to date for IDHPs at the multidrug-resistance transporter (MDR-1), and IDHP-fluorophore conjugates 3c and 7 distribute selectively in SH-SY5Y cells. A homology model for IDHP binding at MDR-1 is presented which represents our current working hypothesis.

4-Isoxazolyl-1,4-dihydropyridines exhibit binding at the multidrug-resistance transporter

The 4-isoxazolyl-dihydropyridines (IDHPs) exhibit inhibition of the multidrug-resistance transporter (MDR-1), and exhibit an SAR distinct from their activity at voltage gated calcium channels (VGCC). Among the four most active IDHPs, three were branched at C-5 of the isoxazole, including the most active analog, 1k.

Dihydropyridines and multidrug resistance: previous attempts, present state, and future trends

Multidrug resistance is defined as the resistance of a tumor cell to the cytotoxic action of divergent drugs used in chemotherapy. Dihydropyridines are a class of calcium channel antagonists that were discovered to have a multidrug resistance reversing effect and prompted investigations resulting in the synthesis of hundreds of new derivatives. Most of the investigators tried to achieve two goals: a decrease in Ca²(+) channel-blocking activity and an increase in the multidrug resistance reversing effect. Most of the synthesized compounds failed in the later stages of studies especially in clinical trials because of pharmacokinetic or pharmacodynamic limitations. Therefore, it will be necessary to include new methods, such as combinatorial synthesis, and, more importantly, to apply computational methods based on global structure-activity relationship models that consider all problems. Moreover, some compounds should be synthesized that are effective on several multidrug resistance targets.

Alkaloids derived from genus Veratrum and Peganum of Mongolian origin as multidrug resistance inhibitors of cancer cells

Alkaloids comprise one of the largest groups of plant secondary metabolites including vinca alkaloids. The ability of six alkaloids from Veratrum lobelianum, one from Veratrum nigrum and three from Peganum nigellastrum to modify transport activity of MDR1 was studied. Flow-cytometry in a multidrug-resistant human MDR1-gene-transfected mouse lymphoma cells (L5178Y) was applied. The inhibition of multidrug resistance was investigated by measuring the accumulation of rhodamine-123 in cancer cells. Veralosinine and veranigrine were the most effective resistance modifiers. In a checkerboard method veralosinine and veranigrine enhanced the antiproliferative effects of doxorubicin on MDR cells in combination. The structure-activity relationships were discussed.

Facile synthesis and antibacterial, antitubercular, and anticancer activities of novel 1,4-dihydropyridines

A series of twenty new 4-substituted-2,6-dimethyl-3,5-bis-N-(heteroaryl)-carbamoyl-1,4-dihydropyridines have been prepared from a three-component one-pot condensation reaction of N-heteroaryl acetoacetamide, an aromatic/heteroaromatic aldehyde, and ammonium acetate under four different experimental conditions. Except for the conventional method, all the experimental conditions were simple, eco-friendly, economical, and the reactions were rapid and high-yielding. The methods employed have been compared in terms of yields, cost, and simplicity. The synthesized compounds were characterized by different spectroscopic techniques and evaluated for their in-vitro anticancer, antibacterial, and antitubercular activities. Amongst the compounds tested, compound 25 exhibited the highest anticancer activity while compounds 14 and 18 exhibited significant antibacterial and antitubercular activities.

Dihydropyridines: evaluation of their current and future pharmacological applications

The 1,4-dihydropyridines (DHPs), a class of drugs, possess a wide variety of biological and pharmacological actions, have represented one of the most important groups of calcium-channel-modulating agents and have experienced widespread use in the treatment of cardiovascular disease. Moreover, it has been demonstrated that DHPs could prove to be highly important as multidrug-resistance-reversing agents in cancer chemotherapy. Recent reports suggest that this class also has other notable activities, particularly as antimycobacterial and anticonvulsant agents. Finally, it might be possible for the DHP motif to serve as a scaffold for other pharmacological applications.

Bis-enaminone based parallel solution-phase synthesis of 1,4-dihydropyridine derivatives

Two variations of a parallel solution-phase synthesis of N-substituted dimethyl 4-oxo-1,4-dihydropyridine-3,5-dicarboxylates 4 and methyl 3-oxo-3,5-dihydro-2H-pyrazolo[4,3-c]pyridine-7-carboxylates 9 from dimethyl acetone-1,3-dicarboxylate (1) were developed. The first synthetic method comprises preparation of the bis-enaminone reagents 2 and 8 and their cyclization with primary amines 3 via double substitution of both dimethylamino groups to give dihydropyridines (DHPs) 4 and 9, respectively. Another variation consists of preparation of the monoenaminone reagents 5 and 10, followed by substitution of the dimethylamino group with primary amines 3, and cyclization of the so formed intermediates 6 with N,N-dimethylformamide dimethylacetal (DMFDMA). In this manner, a library of 46 analytically pure compounds, 24 intermediates 6, 11, and 13, and 22 final dihydropyridines 4 and 9 was obtained employing just a simple filtration workup.

Enantioselective organocatalytic Hantzsch synthesis of polyhydroquinolines

The four-component Hantzsch reaction provides access to pharmaceutically important dihydropyridines. To expand the utility of this method, we have developed a route under organocatalytic conditions with good yields and excellent ee's. Through catalyst screening, we found that a BINOL-phosphoric acid allowed enantioselective synthesis of six-membered heterocycles with a variety of substitution patterns.